| Hot wide strip endless rolling is a cutting-edge technology in the steel industry.In2009,Italian Arvedi company developed the world’s first ESP endless continuous casting and rolling line,in 2015 Rizhao Steel of China introduced the ESP line,in 2019 the ESP lines of Shougang Jingtang MCCR and Donghua steel DSCCR were put into operation successively.By 2021,China has built 9 ESP lines with an annual production capacity of nearly 20 million tons,making it the country with the largest and most complete endless rolling lines in the world.Endless rolling technology has short metallurgical process,high production efficiency,40%-60% energy saving compared with traditional process,high volume production of thin/thin strip,and it is the main representative of low carbon metallurgical technology.However,endless rolling technology has appeared in the world for only ten years,the metallurgical process is obviously different from the traditional continuous casting and rolling,and the research on the metallurgical material formation mechanism and process control is still far from enough.Due to the high casting speed of slab,rigid connection between continuous casting,rough rolling,finish rolling and cooling,continuous thermal contact of rolls for several hours,and so on,the strip performance control can’t meet the requirements of production and application,especially for the thin low carbon/micro carbon steel with large demand.To clarify these new topics and to control them effectively have important theoretical and practical significance for the large-scale production of highquality low carbon/micro carbon steel sheet,creating economic benefits,and energy conservation.Based on DSCCR ESP line,this paper studies the process and property control of low/micro carbon steel under ferrite rolling,shape control theory and application.In order to solve the problems of strength,plasticity,formability and poor shape of strip under endless rolling process,the method of combining material basic haracteristics,process model research and production practice is adopted.The main conclusions are as follows.(1)By the analysis of ferrite rolling process,phase transformation,recrystallization and carbide precipitation process of low/micro carbon steel in ESP line,it is shown that the ferrite rolling process and properties control in ESP line must be carried out with the integrated process design,optimization and control from the whole process of slab solidification and soaking,rough rolling,intermediate slab temperature control,finish rolling,cooling and coiling under the high speed condition.(2)The specific scheme of ferrite rolling process design,process and performance control of low/micro carbon steel suitable for the characteristics of DSCCR endless rolling line is put forward: under the high casting speed of 5.3 ～ 5.5 m/min,1# furnace entry temperature is 1020～1040℃,rough rolling delivery temperature is 950～980℃,the final rolling temperature is 780 ～ 810℃,and the coiling temperature is 630 ～ 650 ℃.(3)The microstructure of low/micro carbon steel strip rolled with ferrite rolling technology is ferrite,a small amount of pearlite at the corner of grain and cementite precipitated at the grain boundary.The strip have no obvious layered structure,the ferrite grain size increases by 3～5 μm compared with that of conventional austenite rolling.Tensile strength is more than 340 MPa and elongation is more than 30 ～ 44% for the plate thickness of 3.0 ～ 1.0 mm;strength increases and elongation decreases with plate thickness thinning;plane anisotropy value is lower than that of conventional rolling.(4)The 0.04C-0.2Si-0.4Mn strip rolled with ferrite rolling technology in the DSCCR endless line has the characteristics of high strength and high performance.The yield strength of 1.2～2.0 mm strip is 330～380 MPa,the tensile strength is 400～430 MPa,the elongation is 31～41%,the bending performance is good,the hole expansion rate is larger than 100%,and the lug rate is less than 10%.(5)The final rolling temperature of 0.04C-0.2Si-0.4Mn steel is 800～820℃,and the coiling temperature is 600℃.Using the low-temperature ferritic rolling process can significantly reduce the Energy consumption and oxidative burn loss;the microstructure is ferrite,a small amount of lamellar pearlite and short rod-like cementite;EBSD analysis shows that the small-angle grain boundaries increase significantly for strip gauge less than2.5 mm.(6)An integrated fast calculation model for roll stack and strip deformation of endless rolling line is established,the accuracy and reliability of the model are verified by shape measurement.For the problem of large fluctuation of strip crown in the mass production of same width and thin specification in the endless rolling line,a work roll shifting strategy of double attenuation asynchronous is proposed.It is found that when the number of shifting steps in a cycle is relatively small or large,it is not conducive to the stability of strip crown.On the basis of ensuring the roll shifting range,the smaller the value is and the more conducive to the stability of strip crown and the uniformity wear of roll.(7)The downstream stand of DSCCR endless rolling finishing mills adopts VCR technology,which increases the transverse stiffness of the mill compared with the original roll shape and weakens the influence of rolling force change on the crown fluctuation,therefore,the rolling stability and shape control ability are improved.After adopting the above strategies and technologies,the maximum crown fluctuation in the rolling unit is reduced by 21.05%,the maximum crown fluctuation of adjacent strip is reduced by28.57%,and the wear of work roll is more uniform.100 images;25 tables;158 references. |
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